1. Field of the Invention
The present invention relates to an optical device for irradiating a wafer with a laser beam or beams and a laser beam machining apparatus having the same.
2. Description of the Related Art
In a semiconductor device manufacturing process, a semiconductor work having a roughly circular disk-like shape wherein a plurality of regions are demarcated by streets (cutting lines) arranged in a grid pattern on a face side of the semiconductor work and circuits such as ICs, LSIs, etc. are formed in the thus demarcated regions is cut along the streets to thereby divide the semiconductor work on a circuit basis into individual semiconductor chips. The cutting of the semiconductor work along the streets is normally carried out using a cutting apparatus called dicer, and a machining method of cutting by irradiation with a laser beam has also been conducted (see, for example, Japanese Patent Laid-Open No. Hei 10-305420).
In addition, an optical system in which a laser beam is branched into two laser beams so as to enable simultaneous machining at two locations, for the purpose of enhancing machining efficiency, has also been proposed (see, for example, Japanese Patent Laid-Open No. 2001-121281 and JP-T-2003-531393).